1. Field of the Invention
The present invention relates to a regenerative heat exchanger for gaseous media which are in a heat exchange with one another. The regenerative heat exchanger includes stationary or rotating storage masses and at least one cleaning device for the storage masses, wherein the cleaning device can be pivoted in relation to the annular cross section of the storage masses from the inside toward the outside or vice versa. The regenerative heat exchanger can be used for the preheating of air as well as for the preheating of gas.
2. Description of the Related Art
The air preheater is used in power plant furnaces and industrial furnaces for preheating the combustion air. The gas preheater is used for preheating in the case of exhaust gas purifying processes, for example, in catalytically operating reactors, or for reheating in the case of gas scrubbing processes.
To the extent necessary, the heating surfaces of the storage masses are constructed so as to be resistant to soiling. Usually, the heating surfaces are enameled; in some cases, enameled heating surfaces are used at the hot end and heating surfaces of high-grade synthetic material are used at the cold end. However, for various reasons, a contamination of the heating surfaces cannot be prevented. It has been found that progressive clogging can be caused by very fine dust which is capable of baking from cold dust firings as well as by the precipitation of moisture when the temperature drops below the dew point. Therefore, it is known in the art to carry out a periodic cleaning by means of soot blowers during the operation. For achieving a lasting cleaning effect, the blowing devices are arranged at the hot end and the cold end of the heat exchanger. In the case of persistent contamination, for example, cemented or carbonized contamination, chemical rinsing processes and ultrahigh pressure rinsing processes are available.
In air preheaters or gas preheaters having a rotating heating surface carrier, the soot blower and the rinsing device or a support device for an ultrahigh pressure nozzle lance can be mounted at a fixed location. The cleaning media, such as, superheated steam, compressed air, rinsing water or chemical solutions, are introduced at only one location of the circumference because, due to the rotation of the heating surface carrier and the simultaneous radial adjustment of the blower, the entire heating surface comes within the range of the blow jet. For cleaning air preheaters or gas preheaters which have rotating hoods instead of a stationary heating surface carrier, a blowing device is provided which rotates together with the rotating hoods.
In air preheaters of medium size, a blowing or cleaning device is known in the art which includes a rotatable turnstile with nozzles, wherein the turnstile is rotated during each rotation of the hood by a pin spacing by means of a control wheel provided with a number of pins and a tappet which is displaceably mounted on a stationary housing. On the other hand, large air preheaters are equipped with radially displaceable blow tubes instead of a rotatable turnstile with nozzles. The radial movement of the blow tube is produced by the rotary movement of a control wheel and by a crank drive.
In another embodiment, the air preheaters are equipped with a section blower which is controlled by a rotary valve. In that case, the supply of blow medium is controlled by the rotary movement of a control wheel through a rotary valve in such a way that the section blowers alternatingly direct blow jets against the heating surfaces which are arranged in a ring-like manner (see brochure Rothemuhle,"Regenerativ-Luftvorwarmer", Regenerative Air Preheater!, page 19).
The heating surfaces installed in the regenerative heat exchangers in cylindrical housings, i.e., the heating surface carriers, are usually periodically cleaned, i.e., blasted, for example, every eight hours. It has been found in this connection that there are problems with respect to achieving a cleaning of the heating surfaces which is as uniform as possible over the entire annular cross-section which increases from the inside toward the outside for reasons inherent to the system and that certain areas can be cleaned only incompletely or not at all because of the fact that the blow nozzles and heating surfaces cannot be precisely allocated relative to each other and because of an insufficient supply of blow medium. One reason for this is the fact that the blowers and the heating surfaces are moved relative to each other during cleaning. While the average speeds of rotation do not usually change because of the constant rates of rotation, different circumferential speeds occur between the inner area and the outer area of the annular cross-section of the heating surfaces of the heating surface carrier. In practice, attempts are made to eliminate these problems by carrying out blowing procedures more frequently and for longer periods of time. However, this is usually only partially successful and, therefore, the consumption of blow medium is simultaneously increased to quantities which are not economically feasible.